Objective: Interferon is one of a large number of soluble mediators of cellular immunity (lymphokines) produced by lymphocytes as a result of immune recognition phenomena. It seems likely that it must have some function in the immune system, possibly as a regulator of immune recognition mechanisms. This proposal is to study the role of interferon in immune phenomena. Specifically, this proposal is to study possible effects of interferon on: a) production and action of other lymphokines, especially mitogenic factor, lymphotoxin, and DNA synthesis inhibitor, all of which seem to play a modulating role in lymphocyte proliferation, b) proliferation of lymphocytes, non-stimulated and those stimulated by specific and non-specific mitogens, c) initiation, maturation, proliferation and function of "killer" cells, d) replication of viruses in lymphocytes, both normal and specifically immune, and also stimulated by non-specific mitogens; and especially in conjunction with other lymphokines, and including an analysis of the consequence of virus replication upon lymphocyte function, e) replication of viruses in macrophages and on macrophage function in processing antigens for presentation to lymphocytes.